(1) Field of the Invention
The present invention relates to a cylindrical battery, and particularly relates to a technique for reducing occurrence of defects due to an insulating ring.
(2) Description of the Related Art
In recent years, secondary batteries in various shapes have been widely used in accordance with demand of devices that use the batteries. Meanwhile, the conventional cylindrical shape has versatility, and adopted in various types of batteries, such as nickel cadmium (Ni—Cd) batteries, nickel-metal hydride batteries, alkaline batteries, lithium batteries and lithium-ion batteries.
FIG. 6A is a cross-sectional view of a conventional cylindrical battery 100.
As FIG. 6A shows, the conventional cylindrical battery 100 basically has a structure in which an electrode assembly 120 is housed in a casing 130 filled with an electrolyte, and an opening thereof is sealed with a sealing lid 140.
The casing 130 is formed in a cylindrical shape having a bottom by performing deformation processing on a flat metal plate. The material thereof is a nickel-plated sheet steel, for example.
Also, a short-diameter part 131, where the diameter is locally shorter, is provided near the opening of the casing 130.
An insulating ring 160 which is circular and has insulation properties is provided in a gap between the electrode assembly 120 and the short-diameter part 131.
When the cylindrical battery is given a shock, the electrode assembly 120 sometimes moves in the direction of the axis of the cylinder. The insulating ring 160 is provided for preventing the top end of the electrode assembly 120 from directly contacting the short-diameter part 131.
The sealing lid 140 is formed by affixing a safety valve and so on to a main body formed by performing deformation processing on a material that is the same as the material of the casing 130.
As FIG. 6B shows, a outside diameter D1 of the insulating ring 160 is determined to be shorter than an inside diameter D0 of the casing 130.
This is for inserting the insulating ring 160 into the casing 130 such that the insulating ring 160 is surely placed on the electrode assembly 120.
Although the insulating ring 160 stated above is in a circular shape, it may also be in a shape of a circle that has a plurality of projections from the circumference thereof; an octagon shape, and so on.
Even in the case the insulating ring is in a shape other than the circular shape, the maximum diameter thereof should be shorter than the inside diameter D0 of the casing 130.
However, in the conventional cylindrical battery 100, there is a gap in a direction of the diameter of the casing 130, between an inner wall of the casing 130 and an outer edge of the insulating ring 160. If this gap is wide, there are possibilities, in the manufacturing process for the cylindrical battery 100, that the insulating ring 160 is misaligned, e.g. placed in an inclined condition with respect to the upper surface of the electrode assembly 120, or the insulating ring 160 jumps out of the casing 130 (hereinafter called “the jump-out problem”) due to vibrations of the conveyor line.